1. Field of the Invention
The invention relates to apparatus for separating materials of different densities such as liquids and solids, and more particularly to a centrifuge apparatus for concentrating the solids fraction of a solids-liquid slurry, for example, wherein the concentrated solids fraction is moved to an outlet therefor by means of pressure fluid.
2. Description of the Prior Art
In the broad field of solids-liquid separation, centrifugal separation is a typical mechanical method for achieving the desired objective in an efficient manner. The separation is achieved by apparatus wherein the solids fraction is continuously separated from the liquid fraction of a solids-liquid slurry being treated by the application of high centrifugal force. The slurry is initially introduced into a revolving metallic bowl of a centrifuge through a stationary feed tube at the center of rotation of the apparatus. In operation, the slurry is then acted upon by centrifugal separating forces which often times approaches 3,000 times the force of gravity. The solids are thereby caused to be forced outwardly against the wall of the rotating bowl. Manifestly, the liquid, being of lesser density, forms a concentrated inner layer in the rotating bowl. It will be appreciated that the suspended particles or solids which are more dense than the suspending liquid tend to migrate toward the periphery. The rapidity with which this migration proceeds is dependent upon the intensity of the centrifugal force, the difference between the density of the particle and that of the suspending fluid, the viscosity of the liquid, the size and shape of the particle, and to some extent, the concentration of the particles and the degree to which they are electrically charged. A practically complete separation of the suspending medium and the suspended phase can be produced if the centrifugation is allowed to continue until all particles have collected against the outer wall of the rotating bowl. A partial separation of two groups of suspended particles of different size can be affected by allowing centrifugation to continue, only long enough for all the larger particles to be completely packed into the sediment, since then many of the small particles will still be suspended in the fluid. If purification of the larger, as well as the smaller particles is desired, the supernatant fluid can be drawn off and the sediment resuspended in some suitable liquid and subsequently centrifuged again to effect a further separation. This process may be repeated any number of times.
Finally, the concentrated mass of solids is continuously caused to be removed by a screw conveyor action inside of the rotating bowl. This action is accomplished by a helical metal screw which rotates in the same direction, but at a slightly different speed than that of the bowl. The screw functions as a mechanical conveyor designed so that the solids deposited against the inner wall of the bowl are moved to one end thereof, where they are scraped up and out of the liquid layer. The solids are discharged from the bowl through suitably located outlets which lead to a desired receiving chamber.
The clarified liquid is simultaneously continuously removed as its overflows an adjustable weir at the liquid discharge end of the bowl, which is in communication with suitable discharge casing to conduct the liquid away.
Since the solids are typically abrasive in nature, it will be appreciated that they will have a rather deleterious effect on the wearing properties of the screw conveyor and the inner wall of the associated bowl adversely affecting the separating efficiency and the life cycle of the overall centrifuge apparatus.